For the last 4 days I have had a pain like a burning sensation under my left armpit and the side of my left breat it seems to be getting worse . I have checked for any signs of lumps but can't seem to feel any! What do u think it could be? As it is very uncomfortable and painfull.

It can be due to a number of possible reasons.

Are you, or have you recently been breastfeeding? On any sort of medication? Does the area feel warm to the touch? Any fever or feeling flu like symptoms? Are you due for your period soon? Have you ever felt it before?

Just a few possible causes: a breast infection... even if you have never breastfed, hormone changes if you notice more around your period, certain medications can cause it.

Certainly see your doctor if it continues or worsens.